Admin page without inlines dinamically

Sometimes the related objects needs that the main object exists in order to edit and save them properly.
There are two main solutions: override the ModelAdmin.add_view() view or remove the inlines only from the add view page (and not from the change page). The former requires a lot of coding, the latter it's impossible without patching Django because the inlines are not dynamic.

This simple solution hides the inline formsets only from the add page, and not from the change page. Adding an "if" structure it is possible to choose the inlines to use.

Example use case: when a related inline model have to save a file to a path that needs the ID key of the main model, this solution prevent the user to use the related inline model until the model it's saved.